The export of amino acid in the phloem is altered in wheat plants lacking the short arm of chromosome 7B

Grain protein content is one of the major determinants of the baking and nu tritional quality of wheat. It has previously been reported that the ditelo somic line of wheat (Triticum aestivum L.) CSDT7BL, where the short arm of chromosome 7B is missing, shows a lower grain protein concentration than th e normal line, but a similar grain yield. In the present paper the growth a nd nitrogen (N) metabolism of wheat plants cv. Chinese Spring (CS) and its ditelosomic line CSDT7BL were compared. When plants were grown to maturity in pots with different N supplements, the wild-type line showed a higher gr ain protein concentration and a lower straw N concentration than the ditelo somic line at every N level analysed, suggesting a deficiency in the N remo bilization capacity. When 15-d-old plants were grown in a growth cabinet in pots with sand, and supplied with nutrient solutions of different nitrate concentrations, the ditelosomic line showed no differences in N uptake per unit of root dry weight, nitrate reductase activity, nitrate, total N conce ntration or free amino acid concentration. However, the ditelosomic line sh owed a decreased capacity to export amino acids in the phloem under high N, independently of the N source. This deficiency was also observed under dar k-induced senescence. The diminished export of amino acids to the phloem wa s principally caused by a decrease in the export of Glu, Asp, and Gin. It i s suggested that the decrease in grain protein concentration in the ditelos omic line is a consequence of defective export in the phloem of these amino acids.